During the steps of extrusion, drawing or enameling of wires or cylindrical bars, made of any material, it is often necessary to verify that their diameter is compatible with the desired measurements. For this function, laser or LED (Light-Emitting Diode) light apparatuses are known: these can be scanning types (laser scanner, for example) or can use linear sensors (for example CCD—Charge-Coupled Device or CMOS—Complementary Metal-Oxide Semiconductor) to detect and measure the shadow of the product to be measured, which can be correlated to the size to be measured.
Normally these apparatuses do not need an exact positioning of the object in the measurement field, but it is necessary that the axis of the product to be measured is located substantially at 90° with respect to the scanning plane (laser scanner) or to the axis of the linear sensor; each shift from the perpendicular causes measurement errors that are directly proportional to the diameter and inversely proportional to the cosine of the angle between the axis of the product and the perpendicular to the measuring plane.
Moreover, all these apparatuses must effect the average between numerous individual measurements (scanning) so as to stabilize the measurement and to obtain repeatability values in the order of a micron or less.
In such apparatuses, the wire, or in general the product to be measured, normally in movement, enters into the reading field of the apparatus that supplies the measurement required. These apparatuses are all normally attached to the machine that works the wire or the bar.
Fixed micrometers are able to carry out quality controls while the wire or other cylindrical product advances at considerable speeds, in the order of 30 m/sec. The reading takes place correctly despite the high speed, which in itself does not cause measuring errors, and in many cases irrespective of the vibration of the product. In fact, provided that on average the axis of the product is maintained at 90° with respect to the measuring plane, such vibration induces errors that can in many cases be minimized by the simple mean (laser scanner) or by strobe light techniques (micrometers with LED+CCD, or CMOS).
However, sometimes, it is necessary to carry out this type of quality control at different points of the line, or on different lines. This entails using various fixed micrometers and a consequent increase in production and management costs of the various measuring devices.
Wireless and portable apparatuses are also known, which use laser or LED light, with similar principles to those used in fixed micrometers, but simply miniaturized and battery powered. However, these operate correctly only on condition that the relative position and the orientation between the object to be measured and the measuring device or micrometer, are certain, which cannot be the case when the micrometer is used manually. To overcome this drawback, guide devices are used for the wire, which require contact with the product to be measured; such micrometers cannot therefore be used to measure products in movement or products for which physical contact may alter or damage the product itself.
A mobile micrometer is known for example, with the commercial name of Lear Gun, in which the object to be measured slides on a plastic prism during the reading step. A wireless micrometer is also known, in which the sample to be measured translates on small guide wheels of the wire.
Known portable micrometers therefore require, for a correct alignment of the sample to be measured, physical contact of the wire, or the product in general, with the aforesaid guides. In practice these requirements make it impossible to use these micrometers to measure the product in movement during extrusion, drawing and/or enameling.
It is also known, in the state of the art, to use sensors of the CCD or CMOS type with linear detection or a two-dimensional matrix for reading the image. CCD or CMOS type linear sensors only make detections along a line, by means of a successive series of detections, up to several thousands a second, in order to obtain a single value after the mean, with a high processing speed. CCD or CMOS two-dimensional sensors, or area sensors, require much higher processing and calculation capacities than a linear sensor, since they are equipped with a much higher number of sensitive elements (pixels) than a simple line of n elements (typically n2), with the obvious result of very long processing times.
US 2002/0041381 A1 describes an apparatus for contactless optical measurement of a profile, in which the optical measuring unit develops in an axial direction from the point of generation of the light source as far as a beam splitter without being subjected to any change in direction. The light is generated by a LED source which passes through a light collimation lens in a parallel ray. The parallel ray irradiates the object to be measured, which generates a portion of shadow beyond the object of the measurement. The parallel ray arriving from the object is collected by a reception lens, and is incident on a linear image sensor through the beam splitter and a first diaphragm. Furthermore, the light separated by the beam splitter is incident on the surface image sensor through a second diaphragm.
The diameter is measured by processing the data of the linear sensor, while the purpose of the area sensor is to supply the user with an image (silhouette) of the object near the measuring region, on which image a marker line is superimposed and displayed, corresponding to the real position of the linear sensor; in this way the user uses the marker line as a sight line, to position the instrument exactly in correspondence with the position along the piece where the measurement is to be made. This device is very useful (if not necessary) precisely in LED light micrometers and CCD or CMOS linear sensors, because in these instruments the beam of LED light that “illuminates” the product is very extensive, also in a direction orthogonal to the measuring plane, and this makes it impossible to know, with a certain accuracy, the actual measuring position on the piece. It should be noted that, on the contrary, laser scanning apparatuses project a thin “blade of light” onto the piece to be measured, generally red light, which identifies the measuring position in a very evident way (in reality, it is the mobile scanning beam which, given the persistence of the image in the human eye, is seen as a “blade” of light).
The combination of the two CCD image sensors of the linear type and with a two-dimensional matrix entails long calculation times due to the quantity of data that the image processing electronic component acquires from the image sensors, in particular from the two-dimensional matrix CCD image sensor. Furthermore, since this form of embodiment of optical measurement develops in an axial direction, the measuring apparatus is necessarily very bulky.
Document DE 43 08 082 A1 provides to emit a beam of light generated by an infrared diode. After passing through a lens, the beam is deflected by a first deflector element so that it can hit the object inside the measurement field. The measurement field is delimited on one side by the first deflector element and on the other side by a second deflector element positioned specular with respect to the first deflector element. The beam of light thus composed of light and shadow reaches a second lens and a single two-dimensional matrix CCD image sensor. In the solution described in this document, the measuring apparatus, equipped with a single image sensor, is usable on condition that there is contact between the wire or bar and guide systems, to prevent misalignments between the object to be measured and the beam of light. Moreover, in this case too, using a two-dimensional matrix CCD image sensor entails higher processing and calculation times than a linear CCD image sensor. Consequently, if on the one hand this solution allows to obtain a compact and manageable instrument for measurements in the field, thanks to a configuration that is not developed on a single axis as in US '381, on the other hand it entails longer image processing times and obliges the wire or product to be measured to be in contact with at least one guide element.
Purpose of the present invention is to obtain a portable micrometer for really contactless measurement of elongated elements, also in movement, able to solve the problems described above; in particular, the purpose is to obtain a portable micrometer equipped with a compensation system such as to make the measurement virtually independent of the angle of the product, with an extremely rapid reaction time such as to allow manual use of the instrument, tolerating the inevitable misalignments and random oscillations deriving from such use.
The Applicant has devised, tested and embodied the present invention to obtain these and other purposes described hereafter.